These are the open end large flange style 304 stainless steel rivet nuts and they are ribbed to grip better against rotation with the dimensions as shown in the photo section of this listing:

• What you get: All measurements are approximate.
• Quality: All products are of the high quality and meet the relevant international standards.
• Stock: We carry a large inventory of stock so all orders can be sent within next business day of your payment.
• Postage: All orders will be posted with Australia Post.